The following is a tabulation of some prior arts that presently appear relevant:
U.S. PatentsPat. No.Kind CodeIssue DatePatentee3,356,473A1967 Dec. 5Hull et al.3,650,714A1972 Mar. 21Farkas3,957,461A1976 May 18Lindstrom et al.3,929,432A1975 Dec. 30Caveney3,984,214A1976 Oct. 5Pratt et al.6,663,682B22003 Dec. 16Baldoni et al.4,399,167A1983 Aug. 16Pipkin5,024,680A1991 Jun. 18Chen et al.5,049,164A1991 Sep. 17Horton et al.4,738,689A1988 Apr. 19Gigl et al.5,529,805A1996 Jun. 25Iacovangelo et al.5,626,909A1997 May 6Iacovangelo4,605,343A1986 Aug. 12Hibbs et al.5,833,021A1998 Nov. 10Mensa-Wilmot et al.8,414,986B22013 Apr. 9Keshavan6,592,985B22003 Jul. 15Griffin et al.6,878,447B22005 Apr. 12Griffin et al.
U.S. Patent Application PublicationsPublication Nr.Kind CodePublication DateApplicant20100206941A12010 Aug. 19Egan et al.20120114442A12012 May 10Johansson et al.20130287507A12013 Oct. 31Lind et al.20120103697A12012 May 3DiGiovanni
Foreign Patent DocumentsForeignDoc. NrCountry CodeKind CodePublication DatePatentee0328583EPB11995 Aug. 30Chen et al.
The present disclosure relates to polycrystalline diamond compact (PDC) cutters used in various cutting, grinding, as well as drilling tools such as drill bits, mill bits (heads), and reamers for earth exploration and production. More specifically, the present disclosure relates to protective barrier coatings which are applied to the polycrystalline diamond (PCD) layer surfaces of the PDC cutters to protect the PCD layer from thermal damages during brazing operations and cutting applications, so as to enhance the cutter's performance and operating life.
PDC cutters are well known in prior arts. They comprise a layer or “table” of PCD materials as a cutting element and a cemented carbide material body as a cutter substrate. They are typically cylindrical in shape. The PDC cutters are formed by sintering and bonding together relatively small diamond grains under conditions of high temperature and high pressure in the presence of a catalyst (for example, cobalt, nickel, iron, or alloys or mixtures thereof) to form a table of PCD materials on a cutter substrate. These processes are often referred to as high-temperature/high-pressure (HTHP) processes. The cutter substrate may comprise a cemented carbide material such as cobalt-sintered tungsten carbide. In such the instances, cobalt (or other catalyst material) in the cutter substrate may diffuse into the diamond grains during sintering and serve as the catalyst material for forming intergranular diamond-to-diamond bonds, and the resulting diamond table, from the diamond grains. In other methods, powdered catalyst materials may be mixed with the diamond grains prior to sintering the grains together in an HTHP process.
Alternatively, a PDC cutter can be formed by brazing an unbacked PCD block onto a cemented carbide material substrate. The unbacked PCD block can be formed by sintering individual diamond particles together in an HTHP process in the presence of catalyst materials that promote the intergranular diamond-to-diamond bonds, as described previously.
Thermally stable polycrystalline diamond compact (TSPDC) cutters refer herein to the PDC cutters that have a thermally stable PCD table that contains none or a reduced amount of catalyst materials such as cobalt. Usually, a leaching process is used to remove the catalyst materials in a PCD using an acid solution. The leaching process may be performed on a PCD table of a PDC cutter or on an unbacked PCD block formed by HTHP. For the latter, the leached unbacked PCD block may be subsequently brazed to a cemented carbide substrate forming a TSPDC cutter. Removal of catalyst materials such as cobalt would improve thermal resistance of a PDC cutter substantially, as the catalyst materials would favor graphitization of diamond and develop thermal stresses due to significant difference in thermal expansion coefficient between them and diamond. Usually, leaching a PDC cutter is just to remove catalyst materials around a surface and subsurface layer of a PCD table, that is, partial leaching, while the rest unleached volume of the PCD table remains intact, which keeps a good toughness of the PDC cutter. A leaching depth is generally tens to hundreds of micrometers from the exterior surfaces of a PCD table.
It is a common practice to braze PDC cutters as cutting elements onto various drilling tools such as drill bits, mill bits (heads), reamers, etc. But, the PDC cutters have poor brazing capability and the bonding strengths are low. In addition, tungsten carbide (in a sintered tungsten carbide substrate), diamond (in a PCD table), and cobalt (in both sintered tungsten carbide substrate and PCD table) in the PDC cutters tend to be oxidized and degrade during brazing operations. During their cutting applications, the PDC cutters experience localized high temperatures at their cutting edges where significant amount of friction heat is generated. Especially, diamond is vulnerable in air or an oxygen containing environment at high temperatures, and it tends to be oxidized and graphitize. As a result, the PDC cutters may suffer thermal damages, resulting in their premature failure.
Although PDC cutters are very successful as a cutting element in drilling tools for earth exploration and production, their premature failure still affects performance and efficiency of drilling tools. The protection of the PDC cutters from thermal damages during brazing and cutting applications is still in need.
In fact, it has been recognized that diamond particles degrade and lose during brazing operations and cutting applications when they are embedded in grinding, abrading, or cutting sections of various tools. These problems are commonly addressed by coating the diamond particles with metals or alloys that bond chemically to the particles, and alloy to the bond matrix. Various coatings of metals and alloys in a single layer or multilayer on the diamond particles are developed to enhance bond retention, improve high-temperature oxidation resistance, suppress high-temperature graphitization, and like benefits. Such the coatings are especially useful when fine-grain diamond grits are employed in the various tools. Typical arts in this single diamond grain coating endeavor include U.S. Pat. Nos. 3,356,473 A, 3,650,714 A, 3,957,461 A, 3,929,432 A, 3,984,214 A, 6,663,682 B2, 4,399,167 A, 5,024,680 A, and U.S. Appl. Pat. No. 2010/0,206,941 A1.
Application of coating onto PCD materials and PDC cutters also receives attentions. It is an effective approach for improving processing capabilities and properties of the PCD materials and the PDC cutters. Various coatings of metals, alloys, and compounds are developed for them in prior arts.
Metallic coatings on PCD materials are for improving their brazing capabilities. U.S. Pat. No. 5,049,164 A discloses PCD materials and diamond crystals with multilayer metal coatings for bonding them to a matrix, which comprise a first metal layer of a refractory metal, such as tungsten, a compliant metal layer of copper, and an outer metal layer of a refractory metal such as tungsten, to prevent thermal stress from damaging PCD or diamond. Metallic bonding layers of a metal, such as nickel, are placed between the tungsten and copper layers for improved bonding. The method of manufacturing multilayer metal coatings comprises applying the inner metal layer by chemical vapor deposition (CVD), applying the first bonding layer metal by electrolytic deposition, applying the compliant layer metal by electrolytic deposition, applying the second bonding layer by electrolytic deposition and applying the outer layer by chemical vapor deposition. A superabrasive tool element comprises a coated diamond product bonded either to a matrix comprising tungsten carbide or iron powder or to a cemented tungsten carbide support.
European Pat. No. 0,328,583 B1 relates to a thermally stable PCD (TSPCD) having a metal coating for improving brazing capability and enhancing its bonding strength to a support structure such as a drill bit, wherein the TSPCD refers to as a leached PCD. The TSPCD has a double layer coating including an outer metal portion chemically bonded to a support by means of a metallurgical bond and an inner carbide portion chemically bonded to the diamond element by an atom to atom bond between the carbon of the diamond and the carbide layer. The double layer coating consists of tungsten/titanium, tungsten/chromium or nickel/titanium. The coating has a thickness of 10 μm-30 μm, which is obtained by CVD or fused salt deposition. The coating covers at least the surfaces in contact with the matrix.
Metallic coatings on PCD materials are also for protecting them from oxidation during brazing operations. U.S. Pat. No. 4,738,689 A discloses a coating on porous self-bonded polycrystalline diamond compacts, hereinafter termed “porous PCD”, to improve their oxidation resistance. The porous PCD has a network of interconnected empty pores dispersed throughout, and contains less than about 3% non-diamond phase. It is a kind of TSPCD. All the exterior surfaces of the porous PCD is enveloped with a continuous coating which is effective under metal bond fabrication conditions, so that oxidation of the diamond in the compact does not exceed a threshold level whereat loss of diamond properties of the compact occurs. Metal bond fabrication conditions comprehend an atmosphere containing oxygen or water vapor. Metal coatings are preferred, especially in coating thicknesses in excess of about 8 μm, and applied by a CVD process. The metal coating is selected from the group consisting of nickel, copper, titanium, iron, cobalt, chromium, tantalum, tungsten, niobium, zirconium, vanadium, molybdenum, and alloys, compounds, as well as mixtures including titanium nitride or titanium carbide.
U.S. Pat. Nos. 5,529,805 A and 5,626,909 A disclose a multilayer coating on unbacked tool compacts including PCD and polycrystalline cubic boron nitride (PCBN), which comprises a metal bonding layer and a protective layer, so as to enable the compacts to be brazed in an air environment to a tool support. The metal bonding layer comprises chromium or tungsten-titanium alloys, while the protective layer is selected from silver, copper, gold, palladium, platinum, nickel, and their alloys. Furthermore, the invention teaches heating the metal bonding layer to form carbide or nitride at the interface between the coating and the compact, and heating the protective layer to provide adhesion of the protective layer to the bonding layer.
As described above, the metallic coatings are applied to PCD mainly for improving its brazing capability. The PCD is freestanding without a supporting substrate of a cemented carbide material, whose brazing capability is notorious. In contrast, metals and alloys generally have an excellent brazing and welding capability, as they have an excellent wettability to brazing alloys. A metal/alloy coating on the PCD would improve its brazing capability.
Thick metallic coatings on PDC cutters are used for dissipating heat during cutting application that would cause thermal damages of the PDC cutters, as a metal or alloy is a good heat conductor. U.S. Pat. No. 4,605,343 A discloses an improved PDC cutter with a cemented carbide substrate, which has a metallic heat sink layer with a thickness of between about 0.01 and 0.1 inches (0.254-2.54 mm) (thick coating) covering at least the outer diamond surfaces of the diamond layer. The heat sink layer is selected from the group consisting of copper, tungsten alloyed with cobalt, nickel, iron, and nickel phosphorus alloys. The heat sink layer is bonded to the diamond surfaces via a bonding medium comprising at least one intermediate layer of metal selected from the group consisting of molybdenum, tungsten, titanium, zirconium, and chromium. The heat sink layer is used to dissipate heat generated during cutting.
Compound coatings on PDC cutters are for improving mechanical properties such as toughness and/or wear resistance. U.S. Pat. No. 5,833,021 A discloses a surface enhanced PDC cutter having a coating refractory material to increase operational life. The coating typically has a thickness in the range of between 0.1 μm and 30 μm and may be made from titanium nitride, titanium carbide, titanium aluminum nitride, boron carbide, zirconium carbide, chromium carbide, chromium nitride, or any of the transition metals or Group IV metals combined with either silicon, aluminum, boron, carbon, nitrogen, or oxygen. The coating can be applied using conventional plating or other physical or chemical deposition techniques. The coating is applied only to the cutting face of inserts to be brazed into a bit body to avoid interference of brazing by the coating which may not be wetted by some brazing alloys. The test results indicate that 2 μm thick TiN coating on a PCD table of a PDC cutter increased its cutting capability by 15%.
U.S. Pat. No. 8,414,986 B2 discloses a method of coating a cutting element with refractory materials and diamond-like carbon (DLC). The cutting element is either PDC or PCBN. Plasma enhanced chemical vapor deposition (PECVD) is utilized. Its relatively low processing temperature would benefit to keep integrity of PDC cutters, avoiding any thermal damages during coating.
U.S. Appl. Pat. Nos. 2012/0,114,442 A1 and 2013/0,287,507 A1 disclose a cutting tool insert comprising a body of cemented carbide, cermet, ceramics, high speed steel, PCD or PCBN, and a hard and wear resistant coating. The coating compounds are zirconium aluminum nitride and a NaCl-structured complex metallic compound, respectively. The coatings have a thickness of between 0.5 μm and 10 μm which is applied by PVD for metal cutting application generating high temperatures.
U.S. Appl. Pat. No. 2012/0,103,697 A1 discloses an earth-boring tool PCD insert of having a protective coating disposed over the insert. The coating comprises a ceramic comprising boron, aluminum, and magnesium. The ceramic of boron, aluminum, and magnesium has a low coefficient of friction and a high hardness.
Refractory compounds such as carbide and nitrides have a high hardness and good wear resistance. But, bonding of the compound coating with the PCD and its cutter may not be metallurgical, and thus, its bonding strength is limited.
The present disclosure has a primary objective that protective coatings with excellent oxidation resistance are applied onto PDC cutters to protect them from thermal damages during brazing operations and cutting applications such as oxidation and graphitization of diamond, so as to prolong their service life. In the meantime, a strong metallurgical bonding between the coating and the PDC cutters may be developed by a carbide-forming metal layer. The excellent oxidation resistance of the coatings and their strong bonding with the PDC cutters can guarantee the coatings to remain a longer time to protect the PDC cutters during brazing operations and especially, cutting applications.